i have been trying to make portrait shots of people with blurred backgrounds with my D70 kit lense. no matter how I try I just can achieve any good results. I have tried using camera auto mode, aperture mode,shutter speed mode, nothing helps.How do I do?

The easiest way with your camera is probably to shoot "wide open" in Aperture Priority Mode (smallest F/Stop Number), get close to your subject, putting some distance between the subject and the background (because you want the background to be outside of the DOF range). Experiment with the above calculator, using different focal lengths (amount of zoom), apertures and focus distances,and you'll get a better idea of how it works.

The max focal length of 70mm on the kit lens probably won't be enough for you to get the creamy background blur so desired by portrait shooters. At f/4.5, the max aperture probably won't be wide enough either.

Try JimC's mentioned suggestions, it may get you there - however I don't think it's an issue that can be addressed without throwing money at it (ie. in the form of buying longer/faster tele lenses).

Use the smallest F stop (which is the 2.8, 4.something). The smaller the appeture hole (Fstop 2.8, 4.something) the more light comes in thus result in a lower dept of field, making foreground and background of focal point more blur.

The larger the appeture hole (Fstop 22, 16 etc) the less light comes in thus result in a higher dept of field, making the foreground and background in focus with the focal point.

If you can't achieve the result you want, there are bunch of plugin available for photoshop that does the same purpose

Actually the smaller aperture/f stop/lens opening is the bigger number like 11 16 22 32 ect. If you want to blur the background you should shoot the lens wide open which is the smaller f number like 1.4 2 2.8 4 4.5 etc. Think of it like squinting your eyes. If you squint your eyes you are in effect using the smallest aperture on your eyes and you can focus near and far. If you open you eyes wide you can only focus near or far not both. Same is true for a lens. Think of it as big number big depth of field. Small number no depth so the background will be out of focus.:idea: